FIG. 1 illustrates the top surface of a portion of a conventional heater chip 40, with an arrangement of backside ink trenches, one shown as numeral 46. The backside ink trench 46 receives a supply of ink and couples the ink internally to the individual heater chambers where the ink is nucleated to form a droplet of ink that is jetted from a nozzle plate (not shown), which is situated on the bottom side of the heater chip 40. The backside ink trench 46 can be supplied with an ink having a magenta color. In like manner, the backside ink trench 48 can be supplied with a cyan colored ink, and the backside ink trench 50 can be supplied with a yellow colored ink. Lastly, in the example, the two backside ink trenches 52 and 54 can both be supplied with a black colored ink. The rows and columns of nozzles are located on the bottom surface of the heater chip 40.
Attached to the backside ink trench side of the heater chip 40 is a conventional ink manifold 42, only a portion of which is shown. The length of the ink manifold 42 can be somewhat longer than, or the same length as the heater chip 40. In any event, the ink channels on the bottom of the ink manifold 42 are closed channels, although the cross section shown in FIG. 1 is through the ink channel features. There is thus one ink manifold 42 for each heater chip 40. The staggered heater chips 40 and associated manifolds 42 are mounted to a page wide plastic or ceramic base member (not shown). The base member communicates the supply of the various ink colors from the respective ink supply reservoirs to the ink manifold 42.
The ink manifold 42 includes elongate ink channels that are mirror images of the backside ink trenches 46-54 of the heater chip 40. The manifold ink channel 56 supplies ink to the backside ink trench 46 of the heater chip 40, and ink channels 58 and 60 supply respective colored inks to the associated backside ink trenches 48 and 50. A larger-width ink channel 62 of the manifold 42 supplies black ink to both of the backside ink trenches 52 and 54 of the heater chip 40. The ink manifold 42 is constructed with a number of ink ports on the top side thereof, where each ink port is connected internally to a respective ink channel. In particular, the ink port 64 is coupled to channel 56, ink port 66 is coupled to channel 58, ink port 68 is coupled to channel 60 and ink port 70 is coupled to channel 62. The ink ports are illustrated as being square or rectangular, but could be other shapes. As noted above, situated over the ink manifold 42 is a base member for interfacing the manifold 42 to the different sources of liquid ink.
FIG. 2 is a cross-sectional view through line A-A of FIG. 1. As shown in FIG. 2, the manifold ink channel 56 has a foot-like design, which a heel section 45 and a toe section 47. The other ink channels 58, 60 and 62 have a similar design. There is a known issue where air bubbles are ‘trapped’ in the toe region of the ink channels. Due to the non-uniform velocity field in the channel, air is not completely removed during priming operations. This air bubble grows over time with normal use and frequent maintenance operations are required to keep the air volume at a low enough level to allow defect free print quality.